The invention relates generally to a method and apparatus for making retreaded tires and, more particularly, to a method of and apparatus in which preformed treads may be consistently cut to lengths that provide for improved splicing while maintaining continuous and repeatable patterns across varying retreading conditions.
Retreaded tires provide an economical way to gain additional use from tire casings after the original tread or retread has become worn. According to a conventional method of retreading, sometimes referred to as cold process retreading, worn tire tread on a used tire is removed to create a buffed, generally smooth treadless surface about the circumference of the tire casing to which a new layer of tread may be bonded.
The tire casing is then typically inspected for injuries, some of which may be skived and filled with a repair gum while others may be severe enough to warrant rejection of the casing. After completion of the skiving process, the buffed surface may be sprayed with a tire cement that provides a tacky surface for application of bonding material and new tread. Next, a layer of cushion gum may be applied to the back, i.e., the inside surface of a new layer of tread, or alternatively, the layer of cushion gum may be applied directly to the tacky surface on the tire casing. Conventionally, the cushion gum is a layer of uncured rubber material. The cushion gum and tread may be applied in combination about the circumference of the tire casing to create a retreaded tire assembly for curing. As an alternative, a length of tire tread may be wrapped around the tire casing with the cushion gum already applied. The cushion gum may form the bond between the tread and the tire casing during curing.
Following assembly of the tire casing, cement, cushion gum and tread, the overall retreaded tire assembly may be placed within a flexible rubber envelope. An airtight seal may be created between the envelope and the bead of the tire. The entire envelope tire assembly may be placed within a curing chamber and subjected to a vulcanization process that binds the materials together.
Portions of the above-described method of cold process retreading may be accomplished on a tire builder. Tire builders may include spindles on which a tire and a roll of cushion gum may be mounted. In such tire builders, the cushion gum may be dispensed by hand as the tire is rotated to adhere the cushion gum to the tire casing. After the cushion gum has been applied, the circumference of the tire casing with cushion gum may be measured and an applicable length of tread may be cut.
In such tire building systems, a length of tread is applied to the cushion gum and casing. Variability in the cut length of the tire tread typically requires manipulation of the tread segment around the perimeter of the tire casing and cushion gum to create an appropriately sized splice in which both ends of the tread length abut one another. It is often desirable, for aesthetic and performance purposes, to match the tire tread design at each end of the tire tread length so that where the two ends of the tire tread length match at the splice, the repetitive pattern of the tire tread design is substantially continuous. The complication and difficulty of such procedures is increased because the tread patterns are subject to varying characteristics depending on the cut location. For instance, from a cross-sectional perspective, the tread end surfaces may have varying total surface area quotients, varying amounts of surface area farther from the center of rotation of the tire and closer to the contact surfaces, etc. In the bonding process, such parameters of the multi-dimensional profile of the tread splice may provide for improved operation in the vulcanization process, particularly in relation to use of envelopes and pressure.
Various devices and methods for cutting a tread length to an appropriate size have been proposed in the past. For example, U.S. Pat. No. 6,899,778 (the '778 patent), the contents of which are incorporated herein in their entirety by reference, generally describes a tire builder. The machine may include a rotatable hub for mounting of a buffed tire casing and a cushion gum applicator that may be configured to stretch a length of cushion gum onto a tire casing. A tread dispenser may automatically dispense a length of tire tread based on the circumference of the tire casing or the circumference of the tire casing plus the cushion gum. Thereafter, a tread applicator of the machine may manipulate the length of tire tread onto the cushion gum to accommodate variability in measurements, cutting, etc.
Machines such as described in the '778 patent may rely on semi-automatic or automatic processes when determining what length of tread is appropriate for a particular casing. Such processes typically include measurements providing information indicative of the circumference of the casing as well as the length of tread that is dispensed from a roll. When an approximate length of tread has been dispensed to match the measured circumference of the casing, a manual cutting operation is typically employed to sever a length of tread.
In previously proposed retreading machines and operations, variability in the measurements of the circumference of the casing or of the dispensed length of tread all too often resulted in dimensional variations when cutting the length of tread. Manual intervention in the cutting process of the length of tread to provide a substantially uninterrupted tread pattern around the entire periphery of the retreaded tire is not only inaccurate, but also compounds the dimensional variability in determining the appropriate length of tread that is required. Such intervention often fails to account for the characteristics of the cross-sectional tread and improving the characteristics of the abutting ends of the tread for performance and bonding characteristics. The inaccuracy of the manual cutting operation in matching the tread pattern may adversely affect the service life and aesthetic appeal of the final retreaded tire. In certain instances, the compounded variability in cutting the appropriate length of tread may make the length of tread unsuitable for use on a retreaded tire, thus necessitating the cutting of an additional length. Such rework operations are time consuming, increase the cost of the retreading operation, increase waste, and so forth.